1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus each provided with the electrophotographic photosensitive member.
2. Description of the Related Art
The electrophotographic photosensitive member basically has a support and a photosensitive layer formed on the support. The photosensitive layer is generally formed of a charge generation layer containing a charge-generating material and a hole transport layer containing a hole transporting material, in this order from the support side. Further, in many cases, a layer called an intermediate layer (which may also be called an undercoat layer) is provided between the photosensitive layer and the support. The intermediate layer is required to have an electric blocking function of preventing a hole injection from the support when a voltage is applied to the electrophotographic photosensitive member. The reason for this is as follows. When the hole injection from the support into the photosensitive layer occurs, it causes decrease of the chargeability and image contrast, and especially, when a reversal development system is employed, it causes black dots in a white portion, which degrades image quality.
On the other hand, the intermediate layer is required to have an electric resistance in an appropriate range. This is because when the electric resistance of the intermediate layer is too high, the charge generated in the photosensitive layer is liable to be retained in the photosensitive layer, which easily causes an increase in residual potential, a fluctuation in potential due to the repeated use, and a ghost phenomenon.
Japanese Patent Application Laid-Open Nos. 56-52757 and 02-181158 disclose as the intermediate layer having an electric resistance in an appropriate range and an electric blocking function, an intermediate layers containing a resin and metal oxide particles.
Further, Japanese Patent Application Laid-Open No. 2002-40698 discloses a technology of providing a plurality of intermediate layers containing inorganic compounds having different particle diameters (an inorganic compound particles having a small particle diameter is contained in the intermediate layer on the photosensitive layer side, and an inorganic compound particles having a large particle diameter is contained in the intermediate layer on the support side).
In recent years, the demand for enhancing the image quality of an electrophotographic apparatus is increasing more and more. In particular, the demand for the image quality of a half-tone image and a solid image is increasing in accordance with the coloring (full coloring) of an output image. On the other hand, in the case of performing an image forming wherein only a portion (light-irradiated portion) of one output image is irradiated with light will become half-tone in the next rotation, an allowable range for a phenomenon in which the density of only the portion irradiated with light will become high (positive ghost phenomenon), or, conversely, for a phenomenon in which the density will become low (negative ghost phenomenon), is becoming narrow. Therefore, even if steps are taken to deal with such situation by providing the intermediate layer containing metal oxide particles, or a plurality of intermediate layers containing inorganic compound particles having different particle diameters, the ghost phenomenon may exceed an allowable level although the increase in residual potential and the fluctuation in potential caused by the repeated use can be suppressed.
Thus, under the circumstances in which the demand for enhancing the image quality of the electrophotographic apparatus becomes high, the related arts are not sufficient for the effect of suppressing the generation of the ghost phenomenon (ghost suppression effect), while keeping the electric blocking function.